1. Field of the Invention
The present invention relates to a novel sodium orthophosphate, and to a process for the preparation thereof.
2. Description of the Prior Art
It is known to this art to prepare sodium tripolyphosphate by drying a solution of orthophosphates containing approximately 5 moles of Na.sub.2 O per every 3 moles of P.sub.2 O.sub.5.
It too is known to this art that the solid orthophosphates obtained as precursors of TPP, Na.sub.5 P.sub.3 O.sub.10, whether prepared in rotating or spray dryer, are respectively constituted of more or less intimate admixtures, either of NaH.sub.2 PO.sub.4 and Na.sub.2 HPO.sub.4 or of Na.sub.3 H.sub.3 (PO.sub.4).sub.2 and Na.sub.2 HPO.sub.4.
Also in accordance with the known processes, calcination of these admixtures of orthophosphates results in various pyrophosphates (Na.sub.2 H.sub.2 P.sub.2 O.sub.7 +Na.sub.4 P.sub.2 O.sub.7) or (Na.sub.3 HP.sub.2 O.sub.7 +Na.sub.4 P.sub.2 O.sub.7) in crystalline or amorphous form. The TPP is then obtained by thermocondensation of the admixtures of pyrophosphates. It is therefore clearly apparent that the phosphate impurities which typically accompany the TPP tetrasodium pyrophosphate soluble or insoluble polyphosphates) result from segregation of orthophosphates or pyrophosphates, and are inexorably linked to the particular process employed.
In any event, whatever the particular process employed, the mixture obtained after drying invariably consists of two crystalline entities which are well known and reflected in the Na.sub.2 O/P.sub.2 O.sub.5 /H.sub.2 O equilibrium diagram. Compare also British Patent Specification No. 1,277,067.